This invention relates generally to a method for lining horizontal pipe sections, and more particularly to such a method that is particularly suited to lining aging sections of sewer pipe extending between adjacent manholes, to reduce leakage due to cracking and the like, and to extend the useful life of such pipe sections.
Methods and apparatus for lining horizontal sections of sewer pipe are known, for example, from U.S. Pat. No. 4,985,196, and the references referred to therein. However, these known methods are not entirely satisfactory for a number of reasons, including, for example, the problem that we shall refer to as blistering. In accordance with the known processes, a pipe liner is drawn into a pipe section in a reduced cross section form, most commonly folded into a generally U-shape. This allows the entire lining section to be drawn easily through a sewer pipe section. The lining is then simultaneously softened and expanded by sealing one end, and introducing pressurized steam or another heated fluid into the other end. As the lining expands, it conforms to the inside surface of the sewer pipe section, and expands to a slightly larger diameter just beyond the ends of the section.
In accordance with the method and apparatus described in the aforementioned U.S. Pat. No. 4,985,196, the liner is formed from thermoplastic material having shape memory characteristics, such that the liner has an elastic memory actuable above a certain temperature. The liner is selected to have an outside diameter approximately equal to the inside diameter of the pipe to be lined. The liner is deformed into the generally U-shaped cross section at a temperature at least equal to the memory activation temperature, and cooled to fix the liner in the temporarily deformed, reduced cross section-shape. After the deformed liner has been inserted into the pipe, it is reheated to a temperature at least equal to the memory activation temperature, and the liner returns to its original cylindrical shape.
It is a principal object of the methods and apparatus of the prior art, as well as of this invention, to reline existing sewer pipe sections in situ. Existing sewer pipe sections may have residual effluents present that must be removed prior to installing a liner. While techniques are known for cleaning the sewer pipe sections before installing liners, these methods may not be entirely successful. Lateral service connections from the sewer pipe to adjacent residences or businesses are normally spaced along the length of the pipe. If effluents are inadvertently introduced through such laterals into the pipe during the lining installation process, a small amount of fluid may become trapped between the liner and the interior surface of the pipe. Such residual fluids cause the liner to bulge inwardly from the pipe wall, forming a blister.
The present invention has as an object to provide a method for installing a liner in an existing sewer pipe section that minimizes the formation of such blisters. Further, the present invention aims to provide a method for installing a liner that is relatively easy to implement in the field, use durable components, and provides a consistently satisfactory installation in the face of varying existing conditions within the pipe prior to lining.